string-list: multi-delimiter `string_list_split_in_place()`

Enhance `string_list_split_in_place()` to accept multiple characters as
delimiters instead of a single character.

Instead of using `strchr(2)` to locate the first occurrence of the given
delimiter character, `string_list_split_in_place_multi()` uses
`strcspn(2)` to move past the initial segment of characters comprised of
any characters in the delimiting set.

When only a single delimiting character is provided, `strpbrk(2)` (which
is implemented with `strcspn(2)`) has equivalent performance to
`strchr(2)`. Modern `strcspn(2)` implementations treat an empty
delimiter or the singleton delimiter as a special case and fall back to
calling strchrnul(). Both glibc[1] and musl[2] implement `strcspn(2)`
this way.

This change is one step to removing `strtok(2)` from the tree. Note that
`string_list_split_in_place()` is not a strict replacement for
`strtok()`, since it will happily turn sequential delimiter characters
into empty entries in the resulting string_list. For example:

    string_list_split_in_place(&xs, "foo:;:bar:;:baz", ":;", -1)

would yield a string list of:

    ["foo", "", "", "bar", "", "", "baz"]

Callers that wish to emulate the behavior of strtok(2) more directly
should call `string_list_remove_empty_items()` after splitting.

To avoid regressions for the new multi-character delimter cases, update
t0063 in this patch as well.

[1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strcspn.c;hb=glibc-2.37#l35
[2]: https://git.musl-libc.org/cgit/musl/tree/src/string/strcspn.c?h=v1.2.3#n11

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/t/t0063-string-list.sh b/t/t0063-string-list.sh
index 46d4839194..1fee6d9010 100755
--- a/t/t0063-string-list.sh
+++ b/t/t0063-string-list.sh
@@ -18,6 +18,14 @@ test_split () {
 	"
 }
 
+test_split_in_place() {
+	cat >expected &&
+	test_expect_success "split (in place) $1 at $2, max $3" "
+		test-tool string-list split_in_place '$1' '$2' '$3' >actual &&
+		test_cmp expected actual
+	"
+}
+
 test_split "foo:bar:baz" ":" "-1" <<EOF
 3
 [0]: "foo"
@@ -61,6 +69,49 @@ test_split ":" ":" "-1" <<EOF
 [1]: ""
 EOF
 
+test_split_in_place "foo:;:bar:;:baz:;:" ":;" "-1" <<EOF
+10
+[0]: "foo"
+[1]: ""
+[2]: ""
+[3]: "bar"
+[4]: ""
+[5]: ""
+[6]: "baz"
+[7]: ""
+[8]: ""
+[9]: ""
+EOF
+
+test_split_in_place "foo:;:bar:;:baz" ":;" "0" <<EOF
+1
+[0]: "foo:;:bar:;:baz"
+EOF
+
+test_split_in_place "foo:;:bar:;:baz" ":;" "1" <<EOF
+2
+[0]: "foo"
+[1]: ";:bar:;:baz"
+EOF
+
+test_split_in_place "foo:;:bar:;:baz" ":;" "2" <<EOF
+3
+[0]: "foo"
+[1]: ""
+[2]: ":bar:;:baz"
+EOF
+
+test_split_in_place "foo:;:bar:;:" ":;" "-1" <<EOF
+7
+[0]: "foo"
+[1]: ""
+[2]: ""
+[3]: "bar"
+[4]: ""
+[5]: ""
+[6]: ""
+EOF
+
 test_expect_success "test filter_string_list" '
 	test "x-" = "x$(test-tool string-list filter - y)" &&
 	test "x-" = "x$(test-tool string-list filter no y)" &&